Synchronization failed 404 error

We're trying to sync a file in our media library from Staging to Production, and with this particular file it fails. It strangely gives a "404: Not Found" error. I found an article that recommends upping ASP.NET's default timeouts and max request lengths in Web.config, but this had no effect. The failure happens within 5 seconds of clicking "Synchronize selected", so I doubt that it's a timeout issue. We're (still) using Kentico 6. Here are the error details:

Brenden is probably referring to <httpRuntime maxRequestLength="2097151"> setting. If this is the only media file for which synchronization fails, you might try to increase a value of this key in a web.config file.